Hydrocyanic

Hydrocyanic is the adjective relating to hydrocyanic acid (HCN), a colorless, highly volatile and highly toxic compound. At room temperature it often exists as a gas with a faint bitter almond odor and is highly miscible with water, forming hydrocyanic acid solutions. Its chemical formula is HCN, and it behaves as a weak acid in aqueous solution, partially dissociating to cyanide ions (CN−). Hydrocyanic acid is a key building block in organic synthesis and has a long history of use in industry and science, also earning the historical name prussic acid.

Industrial production of hydrocyanic acid is dominated by catalytic processes, most notably the Andrussow process, which converts methane and ammonia in the presence of oxygen over a platinum catalyst to hydrogen cyanide and water. It serves as a precursor to a wide range of nitrile compounds, including acrylonitrile (used in plastics and synthetic fibers) and adiponitrile (a nylon-6,6 precursor), as well as cyanide salts used in mining and electroplating. These routes underscore hydrocyanic acid’s role as a versatile chemical building block.

Hydrocyanic acid is extremely toxic; exposure can cause rapid asphyxiation by inhibiting cellular respiration. Symptoms range from headache, dizziness, and confusion to seizures and loss of consciousness. It may be inhaled, ingested, or absorbed through the skin. It is heavier than air and can form hazardous vapors when mixed with acids, which liberate additional hydrogen cyanide gas. Safe handling requires proper ventilation, monitoring, corrosion-resistant equipment, and trained personnel; antidotes and medical treatment may include cyanide antidote kits and supportive care.

Natural sources contain cyanogenic glycosides found in some plant seeds, which can release HCN when processed or damaged. Historically known as prussic acid, hydrocyanic acid is now primarily used as a chemical reagent and industrial intermediate rather than as a consumer product.